In a link between a base station and a user equipment according to a related art, channel variation is serious due to mobility of the user equipment. Therefore, in case of downlink, a user equipment performs a channel measurement using a reference signal (RS) received from a base station and is then able to feed back a result of the channel measurement in form of a channel quality index (CQI), a precoding matrix index and the like. If so, the base station is able to perform a link adaptation for a downlink transmission to from the base station to the user equipment based on the feedback information. Since a channel status may vary seriously in accordance with time due to mobility of the user equipment, the user equipment is able to transmit CQI, PMI and the like by performing the channel measurements periodically.
In case of uplink, a base station is able to measure an uplink channel status based on a sounding reference signal (SRS) received from a user equipment. And, a link adaptation for an uplink transmission can be performed through this channel status measurement. For this, the base station is able to periodically allocate sounding reference signals to a plurality of user equipments.
In case that a channel status between a base station and a user equipment is poor, it is able to provide a radio channel having a better channel status to the user equipment by installing a relay node between the base station and the user equipment. If a relay node is introduced on a cell boundary area having a poor channel status from a base station, a faster data channel can be provided and a cell service area can be extended. Thus, the relay node is the technology introduced to get rid of a radio wave shade area in a wireless communication system and is being used widely. A recent relay node scheme continues to be developed into a further intelligent form, whereas a past relay node scheme if limited to a repeater function of amplifying and transmitting a signal simply. Moreover, the relay node technology corresponds to the technology mandatory for the service coverage extension and the data throughput improvement by reducing the cost for the base station establishment and the maintenance expense for a backhaul network in the next generation mobile communication system. In accordance with the ongoing development of the relay node technology, a new wireless communication system needs to support a relay node used by a related art wireless communication system.
In LTE-A system, a link between a base station and a relay node is able to use a backhaul link, while a link between a base station and a user equipment is able to use an access link. Since a relay node plays a role in relaying data, signals and the like received from a base station to a user equipment, a subordinate relay and the like, it can exist in a stationary form that barely has mobility. In case of considering a scenario for arranging a relay node existing in a stationary form, it can be said that a relay node almost has no variation of a channel status in accordance of elapse of time. In particular, the relay node is characterized in that a channel status for a specific frequency band is almost time-invariant.
A relay node, of which channel status is less variant in accordance with time on a specific frequency band, may not need to make a channel measurement report, i.e., a CQI/PMI (channel quality index/precoding matrix index) feedback, repeatedly with a predetermined cycle like the conventional user equipment and base station. This may cause a problem of increasing a resource overhead or a problem of degrading communication performance. Yet, any effort has not been made to research and develop a detailed method for a relay node to feed back a channel status to a base station until now.
A relay node plays a role in delivering data received from a base station to a user equipment within an area and also plays a role in delivering data received from a user equipment belonging to its area to a base station. Yet, since it is not preferable that the relay node receives data, signals and the like from the base station as soon as transmits data to the user equipments, a subframe capable of signal transmission and reception may be limited. Therefore, many efforts need to be made to research and develop a method of allocating backhaul subframes capable of communication between a base station and a relay node and a corresponding signaling method. When an allocation information on an uplink backhaul subframe and a corresponding signaling are not defined in a relay node, if the relay node receives data from a base station and a user equipment simultaneously, it causes a problem that error occurs in the data.